DateUtil = {
    daysOf: function (year, month) {
        let monthToString = month;
        month = Number(month);
        if(month<10){
            monthToString="0"+month;
        }

        // let prefix = year+"\-"+monthToString+"\-"; // 2020-05-
        let prefix = monthToString+"\-"; // 2020-05-
        let lastDay = Tool.daysOf(year,month);
        let res = [];
        for(let i=1;i<=lastDay;i++){
            let is = i;
            if(i<10){
                is = '0'+i;
            }
            res.push(prefix + is);
        }
        return res;
    }
}